Data ghost

A data ghost was the name given to an impression of a living conciousness that sometimes remained in the neural relay of 51st century comm systems after its occupant had died. The dead person would thus be able to think for some time, though they quickly became confused and started to repeat themselves. They could speak trough the speaker, much to the horror of the witnesses to their death. The Doctor described the effect as a footprint on the beach with the tide coming in. (DW: Silence in the Library/ Forest of the Dead)